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Marco
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 25, 2004 - 09:18 am: | 
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I have run accross an inability to adujst the focus on an old Agfa Jsolette Folder with an Apotar F4.5 lens (3 element).
When I try to adjust infinity focus (using a 300mm on a SLR at infinity and viewing through it at the folder's open shutter, to a backlit target in it's film plane) by rotating the front element, the image in my "collimator" never changes in sharpness. It is slightly unsharp no matter how much that front element turns!
I have used this method successfully many times before with different cameras and the transition from sharp to de-focused, is very quick once that front element start to rotate.
I have also flipped the rear element's position but without success. It almost appears as if someone mounted a unit focusing lens into a camera that was desinged for front cell focusing!
Any ideas were I am going wrong?
Thanks |
charlie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 25, 2004 - 10:09 am: |
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The unit focussing lenses in my Agfa Solinettes have a portion of the helicoid visible when you set the focos at 3.5 feet and look in the back. My Isolette (f4.5 Apotar) has no visible helicoid and the rear element does not rotate or move when I focus. Hope this helps. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 25, 2004 - 01:36 pm: |
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Are you sure that it's just the front element which you are moving? In some cases the grease in the helicoid is so terribly hardened that you actually move the first and center element together - in the thread which holds the latter to the shutter. The thread has 0.5mm pitch and if you turn it just 3/4 of a turn it won't move too much and won't have much effect on focussing.
You can check this by removing the focus dial and check whether just the front part or even the flange of the center element is moving.
I encountered similar on an old Balda 35mm folder - thought focussing was smooth when I bought it but found the things described above after returning home.
BTW none of the Isolettes except for the Super-Isolettes uses unit focussing. |
Marco
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 25, 2004 - 02:13 pm: |
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Winfred,
thanks for the suggestion, I will check.
It appeard to me that this was a "two piece" lens. I.e. the front and center element move together on the helical as one piece, but I may be wrong!
I will check tonight. |
rick oleson
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 25, 2004 - 02:15 pm: |
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I think Winfried is right: hardened focus lube is so common in Agfas that it's rare to find one that will turn. I suspect that your focus helical is totally frozen and you're actually unscrewing the whole cell from the shutter, with little effect on focus.
If you unscrew the cell entirely you can warm it up to soften the lubricant and then (you have to remove the numbered focus-scale ring) disassemble it so that you can thoroughly clean out every trace of old grease in it and relubricate it. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 26, 2004 - 12:14 am: |
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Oh no - I never have seen any front element focussing lens where TWO elements are moved. If both elements are moved together on your lens I am almost sure that you are actually turning the center element thread.
Rick is right, there is almost no old Isolette where the focus is NOT frozen. I once encountered a case that could not be solved by any solvent available (I tried everything from lighter fluid over electronic board cleaner to acetone). Finally I decided to heat the two front elements gently with a hot air gun and this worked in some seconds... |
Marco
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 26, 2004 - 07:25 am: |
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yes the two front elements are frozen together. And no amount of soaking in lighter fluid has helped so far. Neither has warming it up to 200F in the oven. The prblem is getting one element hot while the other stays cool so to get a little differential expansion. Will try with the hair dryer after placing in the freezer. I' either crack the glass to bits (but it ain't no Sonnar anyway...)or succeed!
Thanks for all the help! |
rick oleson
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 26, 2004 - 07:38 am: |
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NO, don't do that! no freezer!!!!
It's not a differential expansion problem, it's a softening the adhesive problem. After a good long soak, wrap both elements in rubber and grip both in the jaws of slip joint pliers; then with steady but very firm pressure, unscrew them anticlockwise. The agfa helocoid grease is a very serious adhesive, you need to be firm with it or it will win (of course you still need to be careful, but i have never damaged one). once they are apart you will have access to clean out the residue with lighter fluid... it will take a while, be thorough. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 26, 2004 - 12:13 pm: |
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Even if you are heating BOTH parts the tolerance between the threads will increase. At least I was taught in mechanical design classes at college that all dimensions will increase if components of identical material are heated.
However, Rick is completely right. But you should try to turn the elements when they are hot. As mentioned before, it took two minutes with the hot air gun to heat the lens (mounted in a vise) and to get it loose - I still had to use pliers but heat was more efficient than any of the many solvents I had tried. |
Rob
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, November 14, 2004 - 07:05 pm: |
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I have just done two of these stuck elements and
was ready to try a nuke on them. Nothing worked.
Heatgun,ice,rosinol,acetone,penetrating oil..nothing. I then put the lens in a shallow
metal pan covering the lens with Rosinol(lighter
fluid) and warming it with a small lamp. In a
few hours I had a pan of green grease blobs that were floating out of the threads and was able to unlock the lenses. |
Peter Wallage
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, November 15, 2004 - 12:44 pm: |
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Rob,
I hope you used a 'dull heat' electric lamp and not a flame. Ronsonol, like most lighter fuels, is naptha and VERY flammable. The most I would dare to attempt in the way of heating would be to stand the container over a basin of hot water. Even then I'd do it well away from any ignitable source.
I once saw a flashover from an elecric fire when someone was filling their lighter, fortunately with only singed eyebrows as a result. With highly flammable substances like that you just can't take too many precautions.
Peter |
Scott
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, November 16, 2004 - 01:45 am: |
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Re: being unable to get a focused image at the film plane within the normal range of focus adjustment:
Here's a mistake I have made a couple of times. After removing all three lens elements of a 1950s lens for cleaning, I accidently install the middle element backwards. You can get an image on the film plane, but it will never be sharp. |
Charlie G
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 18, 2005 - 03:50 pm: |
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Thanks to all --- I just bought an Isolette on E-bay for possible black & white "play" and the first thing I noticed was the focus was "balled"
up ---- With everyones help, I think I will be back in business --- I will use a loupe and a piece of ground glass on the focus plane to set the footage ring where it should be --- Make sense??? I really will be using mostly infinity at high F stop so I have a fair margin of error.
Thanks again |
